The objectives of the current work are to place the important field of research on mathematical simulation of the microcirculation on the stronger base and to obtain direct experimental confirmation of the validity of the results. A simplified analysis has been completed which indicates that the resistance to oxygen transfer in the capillaries is much higher than previously reported. Numerical solutions of the partial differential equations of oxygen transport indicate the relative importance of the various parameters and show the need for careful treatment of the oxyhemoglobin diffusion and reaction kinetics expressions. It is proposed to carry out numerical solutions of the equations of oxygen transport in the cylindrical geometry for the ranges of the parameters of primary interest in the microcirculation. Additional approximate analyses will be carried out to estimate oxygen fluxes in the plasma, and to reduce the results of the numerical solutions to forms of practical utility. The experimental work will involve fabrication of 5 to 10 micron diameter capillaries of silicone rubber. Direct determination of hemoglobin saturation changes will be made in red cell suspensions flowing in the capillaries. Measurements of heme absorbance will be used to monitor oxygen transport over a wide range of conditions.